1. Field of the Invention
The present invention is broadly concerned with tamper-resistant switch assemblies for use in high-security contexts where it is not only necessary to detect relative movement between first and second members (e.g., a door and door frame), but also to detect any attempted tampering with the switch assemblies. More particularly, in one aspect the invention is concerned with tamper-resistant switch assemblies which include a tamper-sensing switch component and an actuating component which are relatively shiftable, as well as mounting structure operable to support the switch and actuating components and to prevent removal thereof without significant relative shifting movement which will trigger an alarm. In another aspect, the invention pertains to switch apparatus including a magnetic switch assembly which includes structure permitting fine adjustment of the position of the biasing magnetic component of the switch assembly relative to the opposed operating magnet; in this fashion, the switch apparatus may be tuned as necessary to prevent any defeat owing to use of a defeat magnet positioned between the switch apparatus and operating magnet.
2. Description of the Prior Art
In recent years the Magnasphere Corp. of Brookfield, Wisc. has introduced a series of innovative and highly reliable switch products useful as a part of alarm systems or as proximity sensors. Such Magnasphere switches in general include a hollow housing typically (though not necessarily) formed of electrically conductive material and with one or more conductive electrodes extending into the housing. A shiftable conductive ball is also located within the housing. The ball moves under the influence of magnetic conditions between respective switch states, usually from a position of simultaneous contact with the switch electrodes to a position out of such simultaneous contact. Such switches are referred to herein as “magnetic ball” switches. U.S. Pat. Nos. 7, 291,794; 5,977,873; 6,506,987; 6,603,378; 6,803,845; 7,023,308; and 5,332,992 illustrate various types of magnetic ball switches.
U.S. Pat. Nos. 7,187,259; 7,218,194; and 7,248,136 describe high security switch assemblies making use of magnetic ball switches. High security switches of this type are almost always mounted externally, e.g., external assemblies are mounted in adjacent relationship on a door and door frame. These external switches may also include anti-tamper switch components, see U.S. Pat. No. 5,633,626.
However, externally mounted, high security switches tend to be very unsightly and make easy access for potential tamperers. A particular problem in this regard is that putatively loyal employees may, during business hours or other time when an alarm system is not operational, attempt to tamper with switch components, so as to permit unauthorized entry during non-business hours when the alarm system is supposed to provide security.
Magnetic switch apparatus operable to detect movement of adjacent first and second members (e.g., a door frame and door) typically includes a magnet ball switch mounted on one of the members and an operating magnet mounted on the other. However, such switch apparatus may be subject to defeat if an intruder positions a magnet of sufficient strength in the region between the magnetic ball switch and operating magnet.